1. Field of the Invention
The present invention relates to dye-donor elements for use according to thermal dye transfer methods, in particular to dye-donor elements comprising cyan dyes that have a good hue and favourable stability.
2. Description of the Prior Art
Thermal transfer methods have been developed to make prints from electronic pattern information signals e.g. from pictures that have been generated electronically by means of a colour video camera. To make such prints the electronic picture can be subjected to colour separation with the aid of colour filters. The different colour selections thus obtained can then be converted into electric signals, which can be processed to form cyan, magenta, and yellow electrical signals. The resulting electrical colour signals can then be transmitted to a thermal printer. To make the print a dye-donor element having repeated separate blocks of cyan, magenta, and yellow dye is placed in face-to-face contact with a receiving sheet and the resulting sandwich is inserted between a thermal printing head and a platen roller. The thermal printing head, which is provided with a plurality of juxtaposed heat-generating resistors, can selectively supply heat to the back of the dye-donor element. For that purpose it is heated up sequentially in correspondence with the cyan, magenta, and yellow electrical signals, so that dye from the selectively heated regions of the dye-donor element is transferred to the receiver sheet and forms a pattern thereon, the shape and density of which are in accordance with the pattern and intensity of the heat supplied to the dye-donor element.
The dye-donor element usually comprises a very thin support e.g. a polyester support, which is coated on both sides with an adhesive or subbing layer, one adhesive or subbing layer being covered with a slipping layer that provides a lubricated surface against which the thermal printing head can pass without suffering abrasion, the other adhesive layer at the opposite side of the support being covered with a dye/binder layer, which contains the printing dyes in a form that can be released in varying amounts depending on, as mentioned above, how much heat is applied to the dye-donor element.
A great many of dyes are known, which can be used in dye-donor elements for use according to thermal dye transfer methods. Among these are those described in e.g. EP-A No. 209,990, EP-A No. 209,991, EP-A No. 216,483, EP-A No. 218,397, EP-A No. 227,095, EP-A No. 227,096, EP-A No. 229,374, EP-A No. 257,577, EP-A No. 257,580, JP No. 84/78894, JP No. 84/78895, JP No. 84/78896, JP No. 84/227,490, JP No. 84/227,948, JP No. 85/27594, JP No. 85/30391, JP No. 85/229,787, JP No. 85/229,789, JP No. 85/229,790, JP No. 85/229,791, JP No. 85/229,792, JP No. 85/229,793, JP No. 85/229,795, JP No. 86/41596, JP No. 86/268,493, JP No. 86/268,494, JP No. 86/268,495, and JP No. 86/284,489.
Many of the dyes proposed for use in thermal dye transfer do not have a fully satisfying spectral absorption and extinction coefficient, or they are not sufficiently stable to light.
Outside the art of thermal dye transfer naphthoquinonediimide dyes are known from EP-A No. 0,095,899. They are formed from carboxamidonaphthalene dye precursor compounds in a silver halide photographic material by cross-oxidation during development of the silver halide. In Research Disclosure 22219 (October 1982) p. 350-2 colour-forming carboxamidonaphthalene and carboxamidodiphenylamine dye precursors and carboximide dyes have been described for the same purpose.